High-frequency multiplex signaling system



July 29. 1924.

l I I 1| l Original Filed Sent. 30 Ll'fland L ESPENSCHIED HIGH FREQUENCY MULTIPLEX SIGNALING'SYSTEM mun- 0 OI r n Patented July 29, 1924.

UNITED STATES PATENT OFFICE;

LLOYD ESPENSCHIED, OF QUEENS. NEW YORK, ASSIGNOE AXE RICA! WHORE AND TELEGRAPH COMPANY, A CORPORATION D1 NEW YORK.

- Emir-FREQUENCY MULTIPLE: srdnanme sits-mill" This invention relates to high frequency multiplex signaling system and more particularly to a terminal circuit arrangement embodying the use of'a common translating circuit adapted both to modulate the transmitted current and to demodulate the high frequency .received current. This application is a division of my co-pending a' plication. Serial No. 327,500, filed Septem er 30,

'1919, entitled. High frequency multiplex signaling systems. I

.In the m'ultiplexsignaling systems here tofore used which employ a plurality -.of

carrier currentsof various frequencies, it

has been customary to insert in the transmitting and the receiving-branches of the terminal circuit a translating device individual to each of said branches. It isthe object of the present invention to adapt the terminal circuit arrangement so that the processes of modulation, demodulation and amplification of the various currents in both the transmitting and receiving branches of the terminal circuit may be performed by a single translating device. Although the preferable form of translating device is a single thermionic vacuum tube or a plurality of such tubes in combination adapted to function as a single unit with respect to the two branches of the terminal circuit, yet any well known type of translating device such as the mechanical repeater may be used.

Anbtlier object of this invention is to"devise a circuit arrangement .of the general character described above and adapted-to generate oscillations of the 'carrierffrer.

quericy to be used for modulation. and decdulation of currents impressed upon the the purpose of local modulation and demodulation.

Original application filed September so, 1918, sci-in in. 327,509. Divided and um s i'iuam'uea April 1a, 1921. 8rhl Il'o. 48am.

d Other and further ob'ect s of this inveiv tion will be apparent rom the following description when read in connection with the'attached drawing of which Figure 1 shows' a type of circuit havin a single modulating and demodulating evice, and Figure 2 shows a ty e of circuit characterized by a balance modulating and demodulating device wherein the frequencies representing the amplification components are suppressed and only the side bands of -frequeiicies are transmitted.

Figure 1 shows another variation of the general circuit characterized by the inclusion in the translatin circuit ofran amplifier which is adapter? to amplify both the low frequency and the highirequeucy os-' cillations that may be impressed upon the translating circuit. .A low frequency signalin circuit L is connected with a termina circuit by means of the triple winding transformer T having a network-N associated therewith to balance the line L Associ ated with the branches'of the fourwire circuit are the low fre uency band filters F and F,, and the hig frequency band filters F, and F The out at side of the terminal'circuit is conne'cte with the branch transmission circuit TL, which is in.

nected with the main transmission line by means of the transformer T I A 'networ N is connected with the transformer T to balance the main transmission line Only one terminal circuit is shown connected with the transmission line, but it should be understood that any number of terminal circuits may be connected therewith, depending u on the number of different bands of reque'ncies that may be transmitted over the main transmission line.

A low frequency signaling iineL having inserted therein a low frequency filter F is connected with the main transmission line in order that low frequency signaling currenis may be transmitted simultaneously with the high frequency carrier oscillations. The translating circuit which is bridged across the two-wire sides of the terminal cir-- A a second-transformer T4, a mod ating and demodulating device MD andanoutment low .then will be impressed put transformer T Associated withthe modulating and demodulating device MD is a source of unmodulated carrier oscillations.G. i

vIn the operation of this circuitarranga equency signaling currents impressed upon circuit L, will ass through circuit 1 and be impressed transformer T, upon. the amplifier A 'lhlse amplified-low fnqluency oscillations y means ofthe transformer .T upon the device MI) thereby modulating t e high frequency carrier oscillations also impressed upon the device IMD by the generating circuit G. The modulatedhigh frequency oscillations will be;impressed bv the transformerT, upon circuit 2 and will pass through the high. frequency band filter F, and over the branch circuit TLto the main circuit v Since the filter F is designed to pass only low frequency currentsof, for instance, zero-to 2,000cycles, the modulated high frequency oscillations which are impressedupon circuit 21which, based on a carrier frequency of, say, 10,000 cycles, may be from 8,000 to 12,000 cycles, will not pass through the'filter F into the low frequency lineL If we assume that the filter F is designed to ing 0 frequencies between 8,000 and 10,000 cycles will be suppressed.and only the'band included between 10,000 and 12,000 cycles will be transmitted. If the-filter F, is' designed to transmit-the same band of frequencies, oscillations -of those frequencies which are transmit a band offrequencies ran received over the main line ML and the branch line RL- pass througlnthe filter F cation, Serial No. 327,500,

into the circuit 4, and will be impressed upon the amplifier A, by means of the transformer T-,. This amplifier will amplify the modulated carrier current which will then be impressed by the transformer T; upon the modulating and demodulating device MD,.' Since the oscillations from the generating circuit G are of the-same fre quency asthe carrier oscillations, priorto modulation by voice frequencies, the latter oscillations will-be demodulated,- andthe low frequency modulating current, i. e. the voice frequency, will be impressed upon the circuit 2 and will pass through the low frequency filter F to the'signaling apparatus pressed by means of the transformer T upon" associated with the line Since the modulating and demodulating device MD shown in this figure is not of the duplex type, such as is shown, for example, in Figure 1, of my filed September 30, 1919, in which the carrier oscillations are prevented from passingto the output,

y means of.

i specti substantially prevented. gs a' further pro-- th filter F may be'-.

copending appli-' the oscillations of carrier frequency will, in i fier in-the other terminal circuit, and theamplified unmodulated carrier frequency may be used thereimas the carrier current for the modulation and demodulation of signals in the .terminal circuit at the distant end of'the transmission circuit ML. This method insures the transmission'of the signaling currents from each end by carrier frequencies which are identically the same inmagnitulde thereby avoiding the difiiculty which arises when slight difierencesexist .between .he carrier frequencies transmitted from different ends ofthe same transmission circuit. 7 Since the circuits L imam, are balanced by .the networksN and N, re-

vel singing around the circuit is tection against sin ing, made toexe'lude t e carrier frequencies by making the range of frequencies adapted to pass through the set filter vary, for example. from 10,200 to 12,000 cycles. Figure 2 illustrates a further modification ofthe general circuit which is characterized by the translating circuit common to both the sending and receiving paths of the terutilization of-the principle of multiple balancing whereby a sing e network may be adapted to balance the transmiss on line for a plurality of terminal circuits. v f

In the circuit arrangement shown in Fig- -ure 2, low frequency currents will be received over the line L and passing into the branch 1 and through low frequency filter F, of the terminal circuit A will be imthe oscillating amplifier A,. By means of the-feed backcircuit shown in connection with this amplifier, the'device may bemade to oscillate at the desired carrier frequency. These carrer oscillations, together with the amplified low frequency currents, 'will be minal circuit; by the direct transmission of impressed'by means of transformer T,-upon the modulating and demodulating device MD and-the carrier current will be modu latcd accordingly. This type of balanced tube circuit does not permit the passage therethrough of unmodulated carrier oscillations, so that the transformer T will impress upon the circuit 3.only the bands of modulated frequency which are based upon the carrier frequency, excluding the carrier frequency itself. The high frequency filter will transmit that band of frequencies which it is designed to pass and the'oscillations transmitted will pass over the branch transmiss on line L and the main transmission line ML to the terminal circuit B at the other end of the said transmission line. The oscillatingainplifier A, which is producing oscillations of carrier frequency will transniit this frequency throughthe transformer T, into the branch 2 and then through the high frequency band filter F and over the line L, and ML to the terminal circuit B,

- The band of modulated oscillations and the oscillations of carrier frequency will besimultaneously impressed by means ofthe transformer T, upon .the input branch 4: of

. circuit B and by means of transformer T upon the am lifiei' A,. Since this amplifier A, has-associated withit afeed back circuit which is sharply tuned to carrier frequency, the oscillations of carrier frequency will be .fed back, and will be reamplified thereby.

These oscillations, together with the amplified oscillations of the band of received oi;-

cillations will -be impressed by means of transformer T upon the modulating and demodulating device MD, The band of received oscillations will be demodulated accordingly and the low frequency currents resulting therefrom will pass through the low frequency filter F; into the low frequency line L Low-frequency currents .set up by signalin apparatus connected with the line L will be impressed upon branch 5 of the terminal circuit B, and: passing through the filter F will be impressed upon the amplifier A,. These low frequency osbillations, together with unmodulated high frequency carrier oscillations received from the other terminal A of this circuit. will pass through the said amplifier and will be impressed by the transformer T upon the modulating and demodulating device MD This device is similar to the device Ml) in that it will pass the modulated side bands of the carrier frequency, but will not-transmit the carrier frequency itself. Accordingly the said modu-' lated bands will be impressed by means of the transformer T, upon the branch 6 and oscillations of that band which the high frequency band filter F, is adapted to pass. will be transmitted over the branch 7 and the circuits L M L, L to the branch 8 of the terminal circuit A. These oscillations will pass through the high frequency band filter F and will be impressed upon the oscillatin amplifier A This band of frequencieswifi be amplified thereby and together with the oscillations of carrier. fr uency generated by A will beimpressed li means of .the transformer T, upon the modulating and demodulatin device MD The band of modulated oscil ations will be demodulatedand the low frequency currentresulting therefrom will pass into the circuit 3, and through the low frequency filter F, into the low frequency 'lineL The balanced modulating and demodulating device used in each" of theq in which the amplification components 0 both high'and terminal circuits is of a low frequencies are eliminated so that'under conditions of substantiall rfect balancethe device produces no straig t amplification.

The advantage derived from the use of ty of balanced translating circuit as pli l to the present type of terminal circuit is that it prevents the. circuit from singing; or the high or low frequenc side.- Another important feature disclosed thearound eit circuit arrangement shown in this gur'e consists in the transmission of-the unmodulated carrier current from one terminal circuit to another terminal circuitat theopposite end of the main transmission line, and

the reamplifying of said carrier current at the other terminal so that it maybe used therein as the basis of transmission of the may be utilized to balance the said line for a plurality of terminal circuits. In the said; circuit arrangement a plurality of triple winding transformers are connected with the branch transmission lines, each transformer being individual to a terminal circuit and a network N is adapted to balance the'niain transmission line for all of the terminal circuits associated with the said line, This multiple balancin system ay be termed- Q ill from the dif- :1 bridge type, as distinguish ferential type employing a triple winding transformer common to all terminal circuits,- as, for example, that shown in Fi ure 1 of my co ending applicatiomserial o. 327,- 500, fi ed September-30, 1919. The advantage of the arrangement. shown in Figure 2 arises from the fact that each terminal ci r. cuit is made essentially a separate un' which is conduciveqto flexibility and is vligl'itly more efiicient due'to the greater efiicie'ncy of? .a transformer that is designed forthspgrii as embodied in a particular form and articular freq ency to which the terminal 'cirof a low frequency circuit, a high frequency circuit, afour-wire circuit connecting the said high frequency and low frequency circuits and networks'adapted to balance the said high frequency and low frequency circuits, the said four-wire circuit having associated therewith a translating circuit common to the transmitting and receiving paths and having means to amplify currents imwith the said" high frequency. and low fre hav ng a translating circuit common-to thepressed thereon and means to modulate'and etect the same. l

2. In a signalingsystem, the combination of a low frequency circuit, a high frequency circuit, a. four-wire circuit,- transforming means to connect ,the' said four-wire circuit quency circuits, and networks associated with the said Jtransforming means to balance the said high]frequency circuit and said low frequency circuit, the. said four-wire. circuit transmitting and receiving paths and having means to amplify currents impressed there-- on and means to modulate and detect the amplified currents.

3. In a signaling system, a combination with 'aliigh frequency transmission-circuit of two vvlow frequency signaling circuits,

four-wire terminal circuitsadapted to con nectthe said hi h frequency transmission circuit with eac of said low frequency signaling circuits, one of said four-wire circuits having means associated therewith to generate oscillations of carrier frequency.

and to transmit them over the said trans mission circuit the other of ,said four-wire circuits having means to reamplify oscillations of-thecarrier frequency received over the said .transmission circuit from the said first four-wire'circuit,

4; In a signaling "system, a combination" with a high frequency'transm'ission circuit of two low frequency signalin circuits, and four-wire terminal circuits a apted to connect the said high frequency transmission circuit to each of said low frequency signaling circui'ts,'each of said four-wire circuits being characterized by a ,translating circuit means for modifying currents and also characterized by filters adapted to guide the received and transmitted currents through the said four-wire circuits, one of said four-j wire'circuits having means for generating oscillations of carrier frequency and means cuit comprising'a' receiving path, a transmitting path and a translating circuit com-' mon to both paths and having means for amplifying currents traversing both of said paths and means for modulating and demodulating the said currents.

7. In a signaling system, a four-wire circuit comprising a receivin path and'a transmitting path, and a trans ating circuit common to both paths and having means for rcgeneratively amplifying oscillations of the carrier frequency impressed thereon and means fornnodulating and detecting 'the'curw rentsf'of other. frequencies impressed upon the translatingcircuit by means of thesaid reamplified carrieroscillations. 4

8. In a four-wire" terminal circuit associated with line circuits, the combination with two two-wire branches of aphigh' frequency band filter and a low frequency filter in each of said two-wire branches, transforming means to connect the four-wirecircuit wiith' the said line circuits, a translating circuit, and meansfor impressing upon the translating circuit thecurrents from one of the said two-Wire branches, the said translating circuit comprising a feedback oscillation circuit adapted to generate oscillations of carrier frequency and to amplify all other currents impressed thereon and also comprising a modulating and demodulating device to modulate and detect the currents impressed upon the said translating circuit.

9. In 'a signaling system, a combination with a transmissioncircuit of two four-wire circuits, one four-wire circuit having means for generating oscillations of carrier frequency and vthe other having means for reamplifying oscillations of carrier frequen cy received over the-said transmission circuit from the said first-mentioned four-wire circuit;

'10'. In a carrier current system, the combination With a-high frequency line of alow frequency line, means for modulating currents' flowing from said low frequency line to saidhigh frequency line, said means actinlg also to-d'etect currents flowing from said hig frequency lineto said low. frequency line and an amplifier in series with the said means for amplifying all of said currents.

In testimony whereof, I have signed my name to this specification this l5th day of April, 1921. p

V LLOYD ESPENSCHIED, X 

